Un-hork the bots by removing intermediate files

The new glob tests created tmp/glob-tests as a directory, but the never removed
it. The `make clean` target then attempted to `rm -f` on this, but it couldn't
remove the directory. This both changes the clean target to `rm -rf` tmp files,
and also alters the tests to delete the directory that all the files are added
into.
auto merge of #9018 : alexcrichton/rust/fix-bots, r=huonw

The new glob tests created tmp/glob-tests as a directory, but the never removed
it. The `make clean` target then attempted to `rm -f` on this, but it couldn't
remove the directory. This both changes the clean target to `rm -rf` tmp files,
and also alters the tests to delete the directory that all the files are added
into.